An ink jet recording device of a serial printing system as shown in FIG. 1 includes at least a delivery means for delivering a recording medium in a sub-scanning direction (not shown) and a recording head 1 which is mounted onto a carriage 2 and reciprocates in a main scanning direction orthogonal to the sub-scanning direction. The ink jet recording device has a structure for jetting ink droplets from the recording head 1 at a desired timing according to print data, and allowing the ink droplets to land on a surface of the recording medium, to thereby perform image formation.
In particular, a large ink jet recording device for forming a large image on a relatively large recording medium, which consumes a large amount of ink, includes as an ink supplying source a main tank 5 of a large capacity at an ink jet recording device main body side, and a sub-tank 9 in a midway of an ink supply passage connecting the main tank and the recording head, to thereby supply the ink to the recording head 1.
In the ink supply mechanism of this type, when a state where an amount of the ink sucked from the main tank 5 to the sub-tank 9 is decreased to a remaining amount L is detected by a sensor such as a reflective optical sensor, a pump 8 is allowed to rotate in a positive direction. Then, when a state where an amount of the ink sucked to the sub-tank 9 has satisfied a preferred amount H is detected by the sensor, the rotation of the pump 8 is stopped. In this ink supply mechanism, the ink is continuously sucked as appropriate from the main tank 5 to the sub-tank 9, so the ink amount in the sub-tank can be continuously kept between the remaining amount L and the preferred amount H. Further, the ink sucked to the sub-tank 9 can be stably supplied to a nozzle of the recording head 1.
The recording head in the recording device of this type applies pressure to the ink to jet and disperse the ink. Therefore, in a case where air bubbles are included in the ink, the pressurized state of the ink becomes unstable and jet performance of the ink droplets is lowered, thereby deteriorating a printing quality. Thus, there is adopted a structure in which ink from which dissolved air is eliminated is filled in the ink supply passages 7 and 12. To be specific, as for the main tank 5 serving as the ink supplying source, an ink cartridge in which ink that has been satisfactorily deaerated in a manufacturing process is sealed in a gas-barrier case 5a and in which the gas-barrier case 5a is further packaged is used. Further, as for the sub-tank 9, a flat ink enclosed-type sub-tank or the like is used, in which an ink bag having a flat shape is enclosed and an ink inlet port connected with the enclosed ink bag is formed on an upper end portion in a gravity direction, in order to fill the ink into the ink flow passage without leaving air in the sub-tank during an initial filling of the ink.
As means for supplying the ink from the main tank 5 to the sub-tank 9 as described above, a piston pump, a tube pump, or the like is employed. Of those, the tube pump is becoming a mainstream of suction means in recent years because a suction pressure, a suction amount, a suction velocity, and the like can be easily controlled and the tube pump can be readily manufactured (e.g., JP 11-190280 A).
As shown in FIG. 8, a general tube pump includes, for example, a circular arc-shaped guiding member 16, a tube 14 arranged on an inner circumference thereof, and at least one pressing member (roller) 15 that rotates while pressing the tube against the guiding member 16. The roller 15 moves while squeezing the tube 14, thereby delivering a liquid, a gas, and the like in the tube in a forward direction. It should be noted that, a rubber tube made of silicon rubber, fluororubber, or the like or an elastic resin tube can be used as the elastic tube.
However, in the above-mentioned ink supply mechanism, in the case where the suction pump 8 is allowed to rotate in the positive direction to continuously suck the ink from the main tank 5 to the sub-tank 9 even after the ink remaining amount in the main tank 5 becomes approximately zero, the ink supply passage 7 connecting the main tank 5 and the sub-tank 9, and the main tank 5 are in a negatively pressurized state. Further, when the main tank 5 is removed from the ink supply passage 7, air enters the ink supply passage 7 from an open portion of an ink supply passage 7a from which the main tank 5 has been removed. In addition, when the ink is sucked from the newly-mounted main tank 5 to the sub-tank 9 through the ink supply passage 7, the air that has entered the ink supply passage 7 is delivered to the sub-tank together with the ink. Then, the air that has entered the sub-tank 9 is delivered to the ink jet recording head 1 together with the ink, so the ink cannot be stably jetted.
To avoid this situation, it is possible that the main tank 5 is removed in a state where the ink still remains to some extent to prevent the inner portion of the ink supply passage 7 from being negatively pressurized. However, the main tank 5 is made of a flexible bag, so it is difficult to detect the ink remaining amount. Therefore, the main tank 5 may be replaced while still having a large amount of ink left, resulting in wasteful dumping of the ink.
Therefore, it is an object of the present invention to provide an ink jet recording device capable of preventing air from entering the ink supply passage 7 due to the negative pressure inside the ink supply passage 7 connecting the main tank 5 and the sub-tank 9 when the main tank is replaced, and fully using nearly the whole ink in the main tank 5 without waste until the ink remaining amount in the main tank 5 becomes approximately zero at the time of the replacement of the main tank.